In general, motorized vehicles, such as the conventional automobile, include a powertrain that is comprised of an engine in power flow communication with a final drive system (e.g., rear differential and wheels) via a multi-speed power transmission. Hybrid-type powertrains generally employ an internal combustion engine (ICE) and one or more motor/generator units that operate either individually or in concert to propel the vehicle. That is, power output from the engine and motor/generators are transferred through planetary gearing in the multi-speed transmission for communication to the vehicle's final drive system. The primary function of the power transmission is to regulate speed and torque to meet operator demands for vehicle speed and acceleration.
One premise behind hybrid-type vehicles is that alternative power is available to propel the vehicle, minimizing reliance on the engine for power, thereby increasing fuel economy. Since hybrid-type vehicles can derive their power from sources other than the engine, engines in hybrid-type vehicles typically operate at lower speeds more often than their traditional counterparts, and can be turned off while the vehicle is propelled by the alternative power source(s). For example, electrically variable transmissions alternatively rely on electric motors housed in the transmission to power the vehicle's driveline.
To operate properly, the power transmission requires a supply of pressurized fluid, such as conventional transmission oil. The pressurized fluid may be used for such functions as cooling and lubrication. The lubricating and cooling capabilities of transmission oil systems greatly impact the reliability and durability of the transmission. Additionally, multi-speed power transmissions require pressurized fluid for controlled engagement and disengagement, on a desired schedule, of the various torque transmitting mechanisms that operate to establish the speed ratios within the internal gear arrangement.
Transmissions are traditionally supplied with hydraulic fluid by a wet sump (i.e., internal reservoir) oil system, which is separate from the engine's oil system. The fluid is typically stored in a main reservoir or main sump volume where it is introduced to a pickup or inlet tube for communication to one or more hydraulic pumps. In hybrid-type transmissions, it is conventional practice to have one hydraulic pump assembly that is driven by the engine (e.g., via the engine crankshaft) for supplying hydraulic pressure to the transmission control system. It is also conventional practice to have an additional pump which is driven from alternate power sources so that pressure is available when the engine is not running and the vehicle is in motion.